As many as 5,000 protesters flooded into central Moscow on Monday night, furious over voting irregularities in Sunday’s parliamentary elections. Chanting slogans like “Putin is a thief,” protesters accused the prime minister’s United Russia party of rigging the election. Monitors say they observed blatant fraud, including ballot box-stuffing. Two prominent opposition figures were jailed, along with 300 other protesters. David M. Herszenhorn, reporter for The New York Times, has the latest from Moscow.